The Adsorption-desorption Behavior Of Heavy Metal At Manganese-oxides/water Interfaces

Adsorption is an important process regulating pollutant's environmental behavior. The extent of adsorption-desorption reversibility controls the bioavailability and toxicity of the metals. In this thesis, using macroscopic adsorption-desorption experiments and novel absorption technique( ADIC,CPHS), the behavior of Zn²⁺ and Cu²⁺ adsorption at MnO₂-water and manganite (γ-MnOOH)-water interfaces are studied as function of pH, ionic strength, particle concentration and temperature. The relationships among particle concentration (Cp), initial concentration, reactive path and the adsorption reversibility will give a reasonable explanation. According to different types of adsorbent system, there are three parts in my dissertation: (I) The adsorption and desorption behavior of Cu²⁺ on three different manganeseoxides. Batch adsorption-desorption experiments showed that: (1) Adsorption of the heavy metal ions by δ-MnO2 strongly depended on pH , ionic strength and initial concentration of metal ions. The values of AH showed the endothermic process of Cu²⁺ adsorbed by δ-MnO₂ ( I ) . At pH₅₀,the adsorption capacity of Cu²⁺ on MnO₂ was δ-MnO₂ (â…¡)〉> δ-MnO₂ ( I )〉 α-MnO₂o (2)Macroscopic experiments showed that at pH(50),ionic strength is 0.1M,there were no particle concentration effects (Cp effects) in Cu²⁺-δ-MnO₂ ( I ), Cu²⁺-δ-MnO₂ (II) and Cu²⁺-α-MnO₂ systems. Adsorption in these three systems was largely reversible and the adsorption reversibility was not influenced by the particle concentration.(3) Kinetic process of sorbed Cu²⁺ at manganese oxides-water interfaces were studied using ADIC technique. The change of reactive path didn't cause changes in adsorption reversibility. The Cu²⁺-a-MnO₂ system showed clear initial concentration effect while no initial concentration effect was observed in theCiT-5-MnO2 ( I ) and Cu2+-5-Mn02 (II) system.(4) The circulative pH scanning curves of Cu in aqueous solution on MnO2 were measured at two different scanning states. Start at low pH, little hysteresis of pH-dependent Cu2+ adsorption was observed, while start at high pH, the ratio between strong adsorption site and weak adsorption site changed ,which results in the pH-adsorption isotherm and pH-desorpton isotherm formed closed chain. (II) The adsorption and desorption behavior of Zn2t on manganite (y-MnOOH) and 5-MnO2(III)(1) pH-curves were studied at three ionic strength(0.01mol/L, O.lmol/L, 0.5mol/L NaN03). The results showed that the adsorption capacity increased along with the increase of pH value but unaffected by ionic strength.(2) Based on ADICT, the adsorption of zinc onto manganite (y-MnOOH) was studied, which was an irreversible process. The final equilibrium state of the system was not influenced by the kinetics as well as the paths of adsorption reactions. So no initial concentration effect was observed in this system.(3) Scanning of pH has different effects on reversible system (Zn-y-MnOOH) andirreversible system(Zn-δ-MnO2(IH)..(HI) the effect of PO^and pH on adsorption and desorption behavior of Zn2+ on manganite (y-MnOOH).(1) The pH curves at different condition were measured at Cp=400mg/L, Co=12mg/L. A typical sigmoid curve was observed. The adsorption was affected by phosphate buffer solution. PO43" influenced the adsorption process by changing surface charge.(2) In Zn-y-MnOOH system.adsorption isotherms were studied at three pH(7.0,7.5,8.0) , and with phosphate buffer solution at pH=7.0,7.5,8.0, adsorption isotherms increased with increasing pH.